In which of the following differential cyanosis found ?
**Core Concept**
Differential cyanosis is a condition characterized by a difference in oxygen saturation between the upper and lower limbs. This phenomenon occurs due to a difference in blood flow or oxygenation between the two areas. It is often seen in conditions where there is a significant shunting of blood between the systemic and pulmonary circulations.
**Why the Correct Answer is Right**
The correct answer is **A. Tetralogy of Fallot (TOF)**. In TOF, there is a right-to-left shunt at the ventricular level, which leads to deoxygenated blood being pumped directly into the systemic circulation. This results in differential cyanosis, with the lower limbs being more cyanotic than the upper limbs due to the greater mixing of oxygenated and deoxygenated blood in the lower body. The increased resistance in the pulmonary artery also contributes to the right-to-left shunt.
**Why Each Wrong Option is Incorrect**
**Option B:** This condition typically presents with a left-to-right shunt, resulting in increased oxygenation of the lower limbs, not differential cyanosis.
**Option C:** This condition may present with cyanosis, but it is not typically associated with differential cyanosis.
**Option D:** This condition may present with cyanosis, but it is not typically associated with differential cyanosis.
**Clinical Pearl / High-Yield Fact**
Differential cyanosis can also be seen in patients with coarctation of the aorta, where there is a narrowing of the aorta, leading to decreased blood flow to the lower limbs and increased mixing of oxygenated and deoxygenated blood.
**Correct Answer: A. Tetralogy of Fallot.**